1 files changed, 100 insertions, 1 deletions
diff --git a/avr/z80-if.c b/avr/z80-if.c
index 5a4104d..f36466c 100644
--- a/avr/z80-if.c
+++ b/avr/z80-if.c
@@ -163,7 +163,6 @@ ISR(TIMER4_COMPB_vect)
 
 ISR(TIMER5_COMPA_vect)
 {
-
 	uint8_t i = timer;
 
 	if (i)
@@ -518,6 +517,106 @@ zstate_t z80_bus_cmd(bus_cmd_t cmd)
 	return zstate;
 }
 
+/*--------------------------------------------------------------------------*/
+
+#define DEBUG_FREQ	0	/* set to 1 to debug */
+
+#define debug_cpu(fmt, args...)		                                              \
+	debug_cond(DEBUG_FREQ, fmt, ##args)
+
+#if 0
+static
+char * ulltoa (uint64_t val, char *s)
+{
+	char *p = s;
+
+	while (val >= 10) {
+		*p++ = (val % 10) + '0';
+		val = val / 10;
+	}
+	*p++ = val + '0';
+	*p = '\0';
+
+	return strrev(s);
+}
+#endif
+
+uint32_t z80_measure_phi(uint_fast8_t cycles)
+{
+	uint16_t ref_stop;
+	uint16_t ref_ovfl;
+	uint8_t x_ovfl;
+	uint32_t x_freq;
+
+
+	PRR1 &= ~_BV(PRTIM3);
+	TCCR3A = 0;
+	TCCR3B = 0b000<<CS30;			/* stop counter */
+	TCNT3 = 0;
+	x_ovfl = 0;
+	TIFR3 = _BV(TOV3);
+	ref_ovfl = 0;
+
+	ATOMIC_BLOCK(ATOMIC_FORCEON) {
+		EIFR = _BV(INTF6);					/* Reset pending int */
+		while ((EIFR & _BV(INTF6)) == 0)	/* Wait for falling edge */
+			;
+		OCR4B = TCNT4;
+		TCCR3B = 0b110<<CS30;		/* Count falling edges on T3 (==INT6) */
+		TIFR4 = _BV(OCF4B);			/* clear compare match flag */
+
+		while (ref_ovfl < 60) {
+			if ((TIFR4 & _BV(OCF4B)) != 0) {
+				TIFR4 = _BV(OCF4B);
+				++ref_ovfl;
+			}
+			if ((TIFR3 & _BV(TOV3)) != 0) {
+				TIFR3 = _BV(TOV3);
+				++x_ovfl;
+			}
+		}
+
+		EIFR = _BV(INTF6);
+		for (;;) {
+			if (EIFR & _BV(INTF6)) {
+				TCCR3B = 0b000<<CS30;	/* stop counter */
+				ref_stop = TCNT4;
+				break;
+			}
+			if ((TIFR4 & _BV(OCF4B)) != 0) {
+				TIFR4 = _BV(OCF4B);
+				++ref_ovfl;
+			}
+		}
+	}
+
+	if ((TIFR3 & _BV(TOV3)) != 0) {
+		TIFR3 = _BV(TOV3);
+		x_ovfl++;
+	}
+
+	uint32_t ref_cnt = (ref_stop - OCR4B) + ((uint32_t)ref_ovfl << 16);
+	uint32_t x_cnt = TCNT3 + ((uint32_t) x_ovfl << 16);
+	uint64_t x_tmp = (uint64_t) 100000 * (x_cnt * cycles);
+
+	/* Stop Timer */
+	TCCR3B = 0;
+	PRR1 |= _BV(PRTIM3);
+
+	debug_cpu("\nx_ovfl: %6u, TCNT3: %6u, cycles: %3u\n", x_ovfl, TCNT3, cycles);
+	debug_cpu("ref_ovfl: %6u, ref_...: %6u\n", ref_ovfl, ref_stop-OCR4B);
+	debug_cpu("x_cnt: %9lu, ref_cnt: %9lu\n", x_cnt, ref_cnt);
+
+	x_tmp = (x_tmp * getenv_ulong(PSTR(ENV_FMON), 10, F_CPU) + (ref_cnt / 2)) / ref_cnt;
+
+	/* round to 5 decimal digits */
+	int_fast8_t sc = 5;
+	for ( ; sc > 0 || x_tmp >= 100000; sc--) x_tmp = (x_tmp + 5)/10;
+	x_freq = x_tmp;
+	for ( ; sc < 0; sc++) x_freq *= 10;
+
+	return x_freq;
+}
 
 /*--------------------------------------------------------------------------*/